Tunable microstructured membranes in organ‐on‐chip to monitor trans‐endothelial hydraulic resistance

Tissue engineering is an interdisciplinary field, wherein scientists from different backgrounds collaborate to address the challenge of replacing damaged tissues and organs through the in vitro fabrication of functional and transplantable biological structures. Because the development and optimization of tissue engineering strategies rely on the complex interaction of cells, materials, and the physical–chemical tissue microenvironment, there is a need for experimental models that allow controlled studies of these aspects. Organs-on-chips (OOCs) have recently emerged as in vitro models that capture the complexity of human tissues in a controlled manner, while including functional readouts related to human organ physiology. OOCs consist of multiple microfluidic cell culture compartments, which are interfaced by porous membranes or hydrogels in which human cells can be cultured, thereby providing a controlled culture environment that resembles the microenvironment of a certain organ, including mechanical, biochemical, and geometrical aspects. Because OOCs provide both a well-controlled microenvironment and functional readouts, they provide a unique opportunity to incorporate, evaluate, and optimize materials for tissue engineering. In this study, we introduce a polymeric blend membrane with a three-dimensional double-porous morphology prepared from a poly(ɛ-caprolactone)–chitosan blends (PCL–CHT) by a modified liquid-induced phase inversion technique. The membranes have different physicochemical, microstructural, and morphological properties depending on different PCL–CHT ratios. Big surface pores (macrovoids) provide a suitable microenvironment for the incorporation of cells or growth factors, whereas an interconnected small porous (macroporous) network allows transfer of essential nutrients, diffusion of oxygen, and removal of waste. Human umbilical vein endothelial cells were seeded on the blend membranes embedded inside an OOC device. The cellular hydraulic resistance was evaluated by perfusing culture medium at a realistic transendothelial pressure of 20 cmH2O or 2 kPa at 37°C after 1 and 3 days postseeding. By introducing and increasing CHT weight percentage, the resistance of the cellular barrier after 3 days was significantly improved. The high tuneability over the membrane physicochemical and architectural characteristics might potentially allow studies of cell–matrix interaction, cell transportation, and barrier function for optimization of vascular scaffolds using OOCs

Collagen I based enzymatically degradable membranes for organ-on-a-chip barrier models

Organs-on-chips are microphysiological in vitro models of human organs and tissues that rely on culturing cells in a well-controlled microenvironment that has been engineered to include key physical and biochemical parameters. Some systems contain a single perfused microfluidic channel or a patterned hydrogel, whereas more complex devices typically employ two or more microchannels that are separated by a porous membrane, simulating the tissue interface found in many organ subunits. The membranes are typically made of synthetic and biologically inert materials that are then coated with extracellular matrix (ECM) molecules to enhance cell attachment. However, the majority of the material remains foreign and fails to recapitulate the native microenvironment of the barrier tissue. Here, we study microfluidic devices that integrate a vitrified membrane made of collagen-I hydrogel (VC). The biocompatibility of this membrane was confirmed by growing a healthy population of stem cell derived endothelial cells (iPSC-EC) and immortalized retinal pigment epithelium (ARPE-19) on it and assessing morphology by fluorescence microscopy. Moreover, VC membranes were subjected to biochemical degradation using collagenase II. The effects of this biochemical degradation were characterized by the permeability changes to fluorescein. Topographical changes on the VC membrane after enzymatic degradation were also analyzed using scanning electron microscopy. Altogether, we present a dynamically bioresponsive membrane integrated in an organ-on-chip device with which disease-related ECM remodeling can be studied